1. Field of the Invention
This invntion relates to single sided, high density bubble domain propagation structures, and particularly to a propagation structure used for high density propagation of bubble domains in amorphous magnetic material.
2. Description of the Prior Art
Several copending applications Ser. Nos. 429,018, 429,001 now U.S. Pat. No. 3,914,751, 429,000 U.S. Pat. No. 3,925,768 and 428,972 and now abandoned, all of which were filed Dec. 27, 1973, describe single sided and double sided structures comprised of gapless propagation structures for movement of magnetic bubble domains in a magnetic medium. Additionally, the use of ion implanted disk structures has been described by R. Wolfe et al in the AIP Conference Proceedings, No. 10, Part 1, pg. 339 (1973), ), which Proceedings contain the text of the papers presented at the 18th Annual Conference on Magnetism and Magnetic Materials, held in Denver, Colo., in 1972.
Ion implanted structures are not practical with amorphous magnetic materials since the amorphous structure is often damaged during the ion implantation. Also, there is difficulty in implanting such materials, which is believed due to the high magnetization of these materials. Generally, it is very difficult to obtain implanted layers having in-plane magnetization.
Since ion implantation does not appear to be useful for providing propagation structures for use with amorphous magnetic materials, magnetic overlays and underlays appear to be most preferable. One possibility is the use of a magnetic layer which has apertured propagation elements therein. For instance, a layer of permalloy can have disk-shaped apertures therein for movement of the bubble domains in response to reorientations of an in-plane magnetic field. However, it has been found that such a structure will not provide good bubble domain propagation, since bubble domains often drift from one channel of propagation elements to an adjacent channel of propagation elements, rather than staying along the boundary of their initial propagation channel.
Another type of propagation structure which is possible for bubble domain propagation in amorphous materials is a structure comprising disks of magnetic materials, such as permalloy, which are adjacent to one another. However, it has often been found that bubble domains will not transfer from one magnetic disk to the adjacent magnetic disk as the in-plane magnetic field rotates. Instead, bubbles often tend to keep traveling in circular paths around individual disks during the field reorientations, rather than sequentially transferring from one disk to the next as is required for proper motion.
In order to alleviate the aforementioned problems, the present invention uses a two-layered propagation structure for movement of magentic bubble domains. Although two-layer propagation structures have been known in the art, such structures were not comprised of contiguous propagation elements for high density storage and/or have exhibited one or both of the problems mentioned previously. For instance, U.S. Pat. No. 3,797,001 describes a propagation pattern using embossed elements in two levels. However, these are not contiguous propagation element which exhibit high density storage.
Another propagation structure known in the art is described in U.S. Pat. No. 3,516,077. This propagation structure is comprised of an overlayer of magnetic material and an underlayer of magnetic material, the overlayer and the underlayer being comprised of disk-shaped elements which are separated from one another. This is a double-sided structure which is disadvantageous from a fabrication standpoint, and also suffers from the problem of bubble domains continually circulating around any one of the disks rather than moving from one disk to the next.
U.S. Pat. No. 3,540,019 describes a propagation pattern using etched patterns in a permalloy layer. These are not contiguous elements which will provide high density.
U.S. Pat. No. 3,599,190 describes a laminated propagation structure in which different coercivity materials are used. Different coercivity materials used in combination with permalloy will cause a change in magnetic pole pattern in order to propagate the bubble domains in a desired direction. In contrast with this, the present propagation structure can use the same material in each of the propagation layers in order to facilitate fabrication. Also, the present invention is directed to a high density structure in contrast with this prior art patent.
As is apparent from the foregoing description, the prior art has presented numerous variations in the geometry of the propagation elements used for bubble domain movement and has provided underlayer and overlayer structures. However, high density structures having particular utility for movement of bubble domains in amorphous magnetic materials have not been widely presented, and in particular the problems described previously have not been sufficiently addressed. In contrast with this, the present propagation structure has been demonstrated in the laboratory to provide reliable, high density propagation and is single sided for fabrication ease.
Accordingly, it is a primary object of the present invention to provide a high density propagation structure for reliable bubble domain propagation.
It is a further object of this invention to provide a high density bubble domain propagation structure for movement of magnetic bubble domains in amorphous magnetic materials.
It is another object of this invention to provide a high density propagation structure for moving bubble domains in an amorphous magnetic material, where the propagation structure can be fabricated using a minimum number of masking steps.
It is a still further object of this invention to provide a single sided propagation structure for moving magnetic bubble domains in a magnetic medium, where the propagation elements themselves can have various geometries.
It is another object of this invention to provide a high density, single sided propagation structure for moving magnetic bubble domains in a magnetic medium, where the bubble domains do not drift away from the desired propagation channel and do not continually circulate without moving in a desired direction along the channel.